iphone-ringtone-m4r — SKILL.md style reference: convert audio to iOS .m4r ringtone/text tone with ffmpeg

iphone-ringtone-m4r.md

name	iphone-ringtone-m4r
description	Use when converting an audio file (mp3, wav, m4a, flac) into an iPhone ringtone or text tone, when a .m4r file is rejected by iOS, or when asked to trim/cut a song to a ringtone-length clip for AirDrop, Dropbox, or Finder sync.

iPhone Ringtone (.m4r) Conversion

Overview

iOS ringtones are plain AAC-in-MP4 files with the extension .m4r. There is no special codec — the only real constraints are the container, the extension, and the length limit. One ffmpeg command does the whole job.

Length limits (the thing people get wrong)

Use	Max length	Where it appears in iOS
Ringtone (incoming call)	40 s	Settings → Sounds & Haptics → Ringtone
Text tone / alert	29 s	Settings → Sounds & Haptics → Text Tone

A 29 s file shows up in both lists, so 29 s is the safer default when the user hasn't specified. Anything over the limit is silently rejected on import.

The command

ffmpeg -y -ss 50 -i input.mp3 -t 29 \
  -af "afade=t=in:st=0:d=0.3,afade=t=out:st=27.5:d=1.5" \
  -c:a aac -b:a 192k -ar 44100 -ac 2 \
  -f ipod -movflags +faststart output.m4r

Flag	Why
-f ipod	Required. ffmpeg can't infer a muxer from .m4r and errors out: Unable to choose an output format. ipod is the MP4/M4A muxer.
-ss before -i	Fast input seek. Fade timestamps then count from the cut, not the original file.
-t 29	Clip length. Keep ≤ 29 (text tone) or ≤ 40 (ringtone).
afade out at len - 1.5	Avoids a hard cut at the end. Recompute when -t changes.
-c:a aac -b:a 192k	AAC is what iOS expects. 192k stereo ≈ 700 KB for 29 s.
-movflags +faststart	Moves the moov atom to the front so the file scrubs instantly.

Verify before handing it over:

ffprobe -v error -show_entries format=duration -show_entries stream=codec_name \
  -of default=noprint_wrappers=1 output.m4r
# expect: codec_name=aac, duration=29.000000

Multiple cuts from one source

Give each output a distinct filename — iOS lists ringtones by filename, so ring.m4r and ring-50s.m4r coexist, but re-importing the same name overwrites.

for spec in "0:ring-29s.m4r" "50:ring-50s-29s.m4r"; do
  ss="${spec%%:*}"; out="${spec##*:}"
  ffmpeg -y -v error -ss "$ss" -i ring.mp3 -t 29 \
    -af "afade=t=in:st=0:d=0.3,afade=t=out:st=27.5:d=1.5" \
    -c:a aac -b:a 192k -ar 44100 -ac 2 -f ipod -movflags +faststart "$out"
done

Getting it onto the phone

1. AirDrop — fastest. Send the .m4r; the phone offers "Save to Ringtones".
2. Dropbox / Files app — share → Save to Files, then tap the .m4r in Files.
3. Finder sync — plug in, select the device in the Finder sidebar, drag the file in.

Then: Settings → Sounds & Haptics → Ringtone (or Text Tone).

Common mistakes

Mistake	Symptom	Fix
Omitting -f ipod	Unable to choose an output format for 'x.m4r'	Add -f ipod
Just renaming .mp3 → .m4r	iOS won't list it	Must be re-encoded to AAC/MP4
Clip longer than the limit	File imports but never appears in the list	Trim to ≤ 40 s / ≤ 29 s
-ss after -i with fade offsets from the original file	Fades land in the wrong place	Put -ss before -i; time fades from 0
Reusing one filename for several cuts	Later import replaces the earlier tone	One distinct filename per cut

Alternative: no ffmpeg

macOS ships afconvert, but it needs a pre-trimmed input and can't fade:

afconvert -f m4af -d aac -b 192000 trimmed.wav output.m4r

Prefer ffmpeg unless it isn't installed.